Device to release a self-expanding implant

ABSTRACT

A device to release from an implant bed in the device a self-expanding implant by pulling back proximally, the length of the implant, a rolling membrane with an inner sleeve that extends distally to the distal end of the implant and an outer sleeve that extends proximally, from the distal end of the inner sleeve, the outer sleeve, during said release, pulling the distal end of the inner sleeve back proximally over the abluminal surface of the remainder of the inner sleeve, proximal of its distal end, the device having a slitter, that is caused to move proximally contemporaneously with the outer sleeve, to slit the inner sleeve progressively, starting at a distal point in the inner sleeve, and progressing proximally along the length of the inner sleeve.

PRIORITY

This application claims priority to U.S. Provisional Application No.61/418,657, filed Dec. 1, 2010, and to United Kingdom Patent ApplicationNo. 1020373.5, filed Dec. 1, 2010, each of which is incorporated byreference in its entirety into this application.

TECHNICAL FIELD

This invention relates to a device to release from an implant bed in thedevice a self-expanding implant by pulling back proximally, the lengthof the implant, a rolling membrane with an inner sleeve that extendsdistally to the distal end of the implant bed and an outer sleeve thatextends proximally, from the distal end of the inner sleeve, the outersleeve, during said release, pulling the distal end of the inner sleeveback proximally over the abluminal surface of the remainder of the innersleeve, proximal of its distal end.

Such devices are disclosed in Applicant's earlier WO2010/076052 andWO2010/076057. Other devices that use a rolling membrane are disclosedin, for example, Scimed WO02/38084 and Gore US-A1-2004/0143272. All fourdocuments are incorporated herein by reference in their entirety.

BACKGROUND

Catheter delivery systems for trans-luminal delivery of self-expandingstents have a rich history in the patent literature. Early proposalswere for a simple sheath radially surrounding the radially-compressedstent at the distal end of the catheter system, the sheath being pulledback proximally, to release the stent from its bed, progressively,starting at its distal end of the bed, within the stenting site orstenosis of the bodily lumen in which the catheter delivery system hadbeen advanced. Readers will appreciate that, because the stent isself-expanding, it is pressing on the luminal surface of the surroundingsheath, up to the moment of its release from the sheath. Thus, frictionforces between the stent and the surrounding sheath must be taken intoaccount when devising a delivery system that will allow the sheath toslide proximally over the full length of the outwardly-pushing,self-expanding stent.

The problems of friction will increase with the length of the stent, andthe pressure on delivery system designers is to deliver ever-longerstents. Furthermore, there is steady pressure on stent delivery systemdesigners to come up with systems that have ever-smaller passingdiameters at the distal end of the catheter. The conventional unit ofdimensions for diameters of systems to advance along a bodily lumen isthe “French” which is one third of a millimeter. Thus, one millimeter is“3 French”. To be able to reduce the passing diameter of a deliverysystem, for example from 7 French to 6 French, is a notable achievement.

One way to respond to the challenge of friction forces between aproximally withdrawing sheath and a self-expanding stent confined withinit is to adopt a “rolling membrane” sheath system, in which the sheathis at least double the length of the stent that it surrounds, beingdoubled back on itself at a point distally beyond the distal end of thestent. Then, proximal withdrawal of the radially outer doubled backportion of the sheath length will cause the “rolling edge” between theouter and inner sheath portions to retreat proximally, rollingproximally down the length of the stent, to release the stentprogressively, as with a single layer surrounding sheath.

While the rolling membrane approach might solve the problem of frictionforces between the proximally retreating sheath and the stent radiallyinside it, it replaces that problem with another friction issue, namelythe need for sliding of the cylinder of the outer sleeve of the sheathover the abluminal surface of the remaining inner sleeve of the sheaththat continues to radially constrain the stent within it. It has beenproposed to provide a lubricant between the inner and outer radialportions of a rolling membrane release system, but designers wouldprefer, if possible, to keep to a minimum the use of any extraneouspowder or fluid, including lubricants, at the distal end of a catheter.Further, there is the practical difficulty of incorporating into amanufacturing system a step of distributing lubricant as required,consistently and reliably and economically.

Consistency is important, because of the importance of certainty that,when the medical practitioner takes the decision to deploy theself-expanding implant at the distal end of such a catheter deliverysystem, the components of the delivery system will form as anticipated,every time, to release the implant smoothly and reliably, in the samemanner every time. Any sort of unpredictable friction force is anathemato this objective. Hence, designers of these delivery systems will makeevery effort to minimize the unpredictable effects of friction on therelease performance of their system. This is a tough challenge,particularly with the ever-present pressure to accommodate longer stentlengths and smaller passing diameters.

SUMMARY OF THE INVENTION

It is the proposal of the present invention, expressed broadly, toprovide in a rolling membrane implant delivery catheter, a slitter. Thisslitter is caused to move, during release of the implant, proximallyalong with the outer sleeve of the rolling membrane, thereby to slitlongitudinally and progressively the inner sleeve to facilitate itsproximal withdrawal, sliding over the abluminal surface of the remaininglength of the unslit inner sleeve.

When delivering self-expanding implants, it is of crucial importance toensure that the system will not release the implant prematurely. Withself-expanding stents of ever-greater radial force, confined within arolling membrane of ever-smaller wall thickness, there is an increasingpotential for rupture of the membrane and premature release of theimplant, so the rolling membrane sleeve system must be carefullydesigned to frustrate that possibility. In the present invention, theslitter is arranged to slit the inner sleeve along a line thatprogresses proximally, but that line starts from a point proximal of thepoint at the distal end of the sleeve that will constitute the rollingedge of the sleeve during stent release. The start point is located ator near the distal end of the bed in which the self-expanding implant ishoused within the delivery system. In this way, it is arranged that theslitter does not commence its slitting action until after an initialproximal movement of the actuator that is used to release the implantfrom the bed. Up until that point, just distal of the slitter, thecircumferential integrity of the inner sleeve can be relied upon torestrain the implant and prevent its outward pressure on the innersleeve from initiating splitting of the inner sleeve, prior to intendedrelease of the implant, at the location of the splitter. Once theimplant release actuator has been actuated, however, the rolling edge ofthe rolling membrane starts to move proximally, and the slitter startsto slit the inner sleeve. From then on, the process of deployment of theself-expanding implant features a progressive rolling back of therolling membrane and splitting of the inner sleeve so that, as theimplant progressively expands into its deployed disposition in thebodily lumen, the material of the rolling membrane is progressivelypulled proximally back from the annulus between the implant and the wallof the bodily lumen so that, once the full length of the implant hasbeen released into the lumen, there is no portion of the rollingmembrane remaining within the annulus between the expanded stent and thestented lumen. After that, the catheter delivery system can be withdrawnfrom the bodily lumen, carrying with it the split material of therolling membrane.

It is preferred to use as the material of the rolling membrane acold-drawn polyethylene terephthalate material. For teaching of the useof such material, reference is made to the earlier WO disclosures of thepresent application, noted above. There is in fact a happy conjunctionof material properties, between the cold-drawn PET material and thetechnical features of the present invention, for the anisotropicmolecular lattice of the drawn material facilitates the operation of theslitter.

It is preferred that the inner and outer sleeves of the rolling membranebe contiguous and of the same material. However, it is also contemplatedto use different materials, joined at the distal ends of the respectiveinner and outer sleeves. This would enable the inner sleeve material tobe tailored to the functions of the inner sleeve and the outer sleevematerial to be tailored to the functions of the outer sleeve.

Thinking again about friction forces, in a system without the slitter,one can imagine that any sort of impediment to the proximal movement ofthe outer sleeve will result in greater levels of longitudinal stress inthe outer sleeve of the rolling membrane proximal of the impediment.Such stresses will have a tendency to reduce the diameter of the outersleeve under tension. Any such “necking in” of the outer sleeve will,self-evidently, increase forces of friction between the luminal surfaceof the outer sleeve, sliding over the abluminal surface of the innersleeve. One can readily imagine that, if the situation worsens, then thesystem can “bind up”, preventing any further proximal movement of therolling edge and frustrating the ability of the doctor to release theimplant any further, possibly resulting in breakage of any component ofthe catheter delivery system that is in tension for releasing theimplant, and risk to the patient. With the slitter of the presentinvention, however, the likelihood of such “binding up” is reduced.

Further improvements in the smoothness and reliability of stent releaseare accomplished by providing the outer sleeve with a plurality of slitsthat go through the wall thickness of the outer sleeve and allow thatouter sleeve to “breathe” radially in and out, as it is pulledproximally down the length of the implant bed, during release of theimplant. If one supposes that the implant includes features such asradiopaque markers or membrane coatings, that can give rise to localvariations of implant diameter, then an ability in the outer sleeve to“breathe” radially in and out as it slides proximally over thesediameter variations, will reduce the likelihood of the binding of theproximally retreating outer sleeve on the structure radially inside it,during implant release.

Judicious design of the slits can accomplish the objective ofbreathability of the proximally retreating outer sleeve, without totalloss of the hoop stress in the outer sleeve that will contribute toradial restraint of the radially compressed implant, prior to itsrelease. Note, however, that the slits need not be provided in the innersleeve and that the hoop stress in the inner sleeve, alone, can besufficient to constrain the stent until the moment of its release. Thepresently preferred arrangement of through slits is to provide two ormore sets of such slits, each set being a plurality of the slits,co-linear, and with each slit having a length less than 20% of thelength of the implant bed, and with the slits regularly spaced from eachother by a spacing that is comparable with the length of each slit, butsomewhat less than the length of each slit. In the embodimentillustrated below, there are just two such sets of slits, spaced 180°apart from each other around the circumference of the implant bed, andwith the slits of one set staggered along the length of the sleeve,relative to the slits of the other set. However, three or more sets ofslits can be provided, where the sets of slits are similarly evenlyspaced apart in the circumferential direction and staggered.

Turning to the construction of the slitter, the presently preferreddevice takes the form of a slitting wire that extends distally, beyondthe distal end of the implant bed, but not quite as far distally as therolling edge of the membrane prior to actuation of the stent releasemeans. This wire lies against the luminal surface of the inner sleeveand passes through a hole in the inner sleeve, close to its distal end,then returning proximally, in the space between the inner and outersleeves, back to a proximal end where it is secured to the device thatwill, at the moment of implant release, pull the outer sleeveproximally. The pulling of the wire proximally, contemporaneously withthe outer sleeve, will cause the wire to slit the material of the innersleeve, commencing at a point on the circumference of the hole that isat the proximal-most point of that circumference and progressingproximally, parallel to the longitudinal axis of the delivery system.Just as the membrane has a rolling edge, so does the slitting wire, atthe point where it doubles back on itself, as it passes from inside theinner sleeve to radially outside it. This rolling edge moves along thelength of the wire, as the wire “rolls” over the inner sleeve.Simultaneously with this slitting, the rolling edge of the rollingmembrane is moving proximally, thereby resulting in the slit portion ofthe inner sleeve radially overlying the remaining unslit portion of theinner sleeve, until the full length of the implant has been released.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal diametral section of the distal end of a firstembodiment of stent delivery catheter system;

FIG. 2 is a view of the distal end of FIG. 1, along arrow II, partly insection

FIG. 3 is a view of the distal end of a second embodiment of a stentdelivery catheter system, looking into the plane of the paper; and

FIG. 4 is a lateral view of what is shown in FIG. 3, from a viewpoint90° away from the FIG. 3 viewpoint.

DETAILED DESCRIPTION

Looking first at FIG. 1 we see a self-expanding stent 10 radiallyconfined within a rolling membrane 12 which features an inner sleeve 14,an outer sleeve 16 and a rolling edge 18 distal of the bed 20 thatreceives the stent 10. The bed 20 is on a shaft 22 that defines aguidewire lumen 24 and carries an atraumatic tip 26 that has a rebate 28to receive the distal end of the rolling membrane 12 and the rollingedge 18.

At the proximal end of the inner sleeve 14, the rolling membrane 12 issecured at an annulus 30 to the shaft 22. The other end of the rollingmembrane 12 extends along the shaft proximally until its end 32 isproximal of a collar 34 that is freely slidable on the abluminal surfaceof the shaft 22. The membrane 12 is secured to the abluminal surface ofthe collar 34. The collar 34 is on the distal end of a pull wire 36 thatruns all the way to the proximal end of the catheter delivery system ofwhich the distal end is shown in FIG. 1. The reader will appreciatethat, when the time comes to release the stent 10, actuation isaccomplished by pulling proximally on the pull wire 36, to pull thecollar 34 proximally and in turn cause the rolling edge 18 of themembrane 12 to advance proximally, all the way down the length of thestent bed 20 and stent 10. A casing tube 38 defines the passing diameterof the shaft of the catheter system. Into the distal end 40 of thecasing tube 38 is drawn, during release of the stent, the length of theouter sleeve 16 of the rolling membrane 12 and, after that, much of thelength of the inner sleeve 14, until the rolling edge 18 has cleared theproximal end of the stent 10. Readers will appreciate that this processputs the loose material of the rolling membrane 12 snugly inside thecasing tube 38 so that, when the catheter system comes to be withdrawnfully from the patient, the loose folds of the relaxed rolling membrane12 will not be dragging along the tissue that defines the walls of thelumen in which the catheter system has been advanced.

So far, the description of the operation of the system is as inapplicants prior published WO2010/076052, from which the basic elementsof FIG. 1 are borrowed.

But now suppose that conditions are artificially manipulated, to makethem excessively more demanding. Perhaps the rolling membrane is toothin, or the stent 10 has excessive radial force and is longer than isshown in FIG. 1. Conceivably, when pulling on the pull wire 36, someimpediment then arises, to the proximal movement of the rolling edge 18,long before that edge 18 has cleared proximally the proximal end of thestent 10. Once the material of the outer sleeve 16, close to the rollingedge 18 begins to bind on the material of the inner sleeve 14, there isa possibility that material in the outer sleeve 16, proximal of thepoint of binding, will neck in under the higher levels of longitudinalstress in which it finds itself. Pursuing our imagination, when thewhole system binds up, in this way, it might be with a long stent onlypartially released to the bodily lumen, with the proximal portion of thestent still captured within the catheter delivery system, and no evidentway for the doctor to complete the release of the stent. Such situationsare not tolerable. They can be managed by the modification andimprovement now to be described.

Attention is again directed to FIG. 1. We see a portion of the shaft 22and the bonding 30 of the proximal end of the inner sleeve 14 to theshaft 22. Again, the proximal end of the outer sleeve 16 is bonded tothe collar 34 which is free to slide on the length of the shaft 22.

A slitting wire 50 is bonded, with the inner sleeve 14, to the shaft 22at the annulus 30. It advances distally, radially inside the innersleeve 14, as far as a hole 52 in the rolling membrane 12 (FIG. 3)proximal of, but near to, the rolling edge 18. The wire 50 doubles backon itself at that point, and returns proximally, all the way to thecollar 34, between the inner 14 and outer 16 sleeves. Note how thesection of FIG. 1 includes both the pull wire 36 and the slitting wire50, meeting at the collar 34.

Note also that the slitting wire 50 is free of slack, between the hole52 and the collar 34, so that the wire 50 begins to slit the membrane 12at the edge of the hole 52 as soon as there has been some proximalmovement of the collar 34 that imposes sufficient tension on the wire50. The reader will recall that the self-expanding implant is imposingan outwardly directed radial force on the inner sleeve 14, putting it intension and facilitating the task of the wire 50 to slit the membrane.The reader will also understand that, from the first proximal movementof the collar 34, longitudinal slitting of the inner sleeve 14 isoccurring contemporaneously with proximal movement of the rolling edge18 of the membrane. In this way, any hoop stress in the proximallyretreating outer sleeve 16 proximal of the rolling edge 18 willgradually reduce once the rolling edge is proximal of the hole 52, asprogressively more and more of the length of the outer sleeve, rolledback from the inner sleeve 14, is slit by the wire and so unable tocontribute any further hoop stress. The progressive loss of hoop tensionin the outer sleeve 16 reduces the likelihood of the outer sleeve 16attracting enough frictional resistance for it to “bind up” on theabluminal surface of the inner sleeve 14 and frustrate further proximalmovement of the collar 34.

The preferred slitter at the moment is the slitting wire shown in FIGS.1 and 2. However, other slitters are contemplated. For example, theouter sleeve 16 could carry near its distal end a small cutting edge orhook that scores or slits the material of the inner sleeve 14. As therolling edge 18 moves proximally down the length of the inner sleeve 14,so does the slitter located on the outer sleeve 16 proximal of therolling edge 18, thereby to score or slit the inner sleeve 14, throughthe full length of the stent bed.

Turning to the embodiment of FIGS. 3 and 4, we see the same slittingwire 50, hole 52 and inner sleeve 14.

FIG. 3 looks at the rolling membrane from radially outside, so we seethe abluminal surface of the outer sleeve 16 and the rolling edge 18. Wesee five short slits 60 that, in aggregate, extend over the full lengthof the stent bed 20. The slits are shown all the same length butoptimization of design might lead to a solution in which the slits aredifferent lengths. Likewise, the gap 66 between each of the co-linearslits 60 of the line of slits might be a different length of gap betweenany two slits but, in the simple situation shown in FIG. 3, each of thegaps is the same length, about one third of the length of each slit.

In the FIG. 4 view, 90° around the circumference from the view of FIG.3, we see a second set of co-linear slits 62 with gaps 64 in betweenthem. One should note that the slits 62 are longitudinally staggeredrelative to the slits 60 of FIG. 5 so that in any transverse sectionthat includes a gap 64, there is present a slit 60. In any transversesection that includes a slit 62, there is a gap 66 between the slits 60above and below the plane of the section on the other side of thecircumference of the sleeve 16.

The reader is invited to contemplate the situation that the implantinside the rolling membrane shown in FIGS. 3 and 4 has at points spacedfrom both its ends one or more zones of somewhat greater outsidediameter than the nominal diameter. Such rings of marginally greaterdiameter can be a source of friction and possibly resistance to furtherproximal sliding movement of the outer sleeve 16. However, the presenceof the slits 60, 62, would allow a degree of diametral expansion notavailable without the slits 60 and 62, for the outer sleeve 16 to easeoutwardly as it slides over the zone of greater diameter within itslumen. The phenomenon has been recognized by the present inventors andhas been named “breathing”. With the slits, the outer sleeve can“breathe” as required, as it proceeds proximally during release of thestent.

Staggering of the sets of slits as described earlier can reduce oreliminate any longitudinal portions of the sleeve along the length ofthe stent bed that are not slit at some point along their circumference.This advantageously contributes to the “breathing” effect.

Summarizing, taking the rolling membrane concept of FIG. 1, and applyingit to ever-longer self-expanding stents of ever-greater radial force andever-greater component complexity will place ever-increasing demands onthe delivery systems designer to ensure that there is no binding up ofthe rolling membrane during progressive release of the implant. Thesimple system of FIG. 1 can be rendered more tolerant of variations ofdiameter of the implant within the membrane, and of unpredictability ofmaterials performance in the material of the membrane itself, byincluding a slitter in accordance with the present invention. Endowingthe outer sleeve with a “breathing” capability will further enhance theperformance of the system and allow its application to ever-longerstents of a greater structural complexity and performance capability.

This detailed description concentrates on the components of theinventive concept. Readers will well understand that all sorts ofvariations and modifications are open to them. Readers who areexperienced in the design of delivery systems for self-expandingimplants will have their own suite of design expertise and capabilities.They will know how to take the inventive concept of the presentinvention and utilize it within the constraints of their own systemarchitectures.

Further, experienced readers are knowledgeable in choice of materialsfor implant delivery systems, and in the design judgments that areroutinely made when putting together the elements of a function systemthat will deliver performance enhancements.

1. An implant delivery device, comprising: a rolling membrane with an inner sleeve that extends distal of a distal end of an implant positioned over an implant bed, and an outer sleeve that extends proximal of a proximal end of the inner sleeve; and a slitter that moves proximally contemporaneously with the outer sleeve portion upon proximal movement thereof, the slitter slitting the inner sleeve beginning at a distal point of the inner sleeve and progressing proximally along a length of the inner sleeve.
 2. The implant delivery device according to claim 1, wherein the outer sleeve includes a plurality of slits, each having a length which is less than 20% of the length of the implant bed, and each of which permits by the opening up of a gap between facing surfaces of the slit, a local temporary increase in the diameter of a portion of the outer sleeve that includes the slit as that portion of the sleeve advances proximally over a zone of larger diameter of the implant within a lumen of the outer sleeve.
 3. The implant delivery device according to claim 2, wherein a first set of said plurality of slits is arranged co-linear along a length of the outer sleeve, and a second set of said plurality of slits is arranged co-linear to the first set and evenly spaced therefrom.
 4. The implant delivery device according to claim 1, wherein the slitter is arranged such that its slitting action commences at a point that is at or near a distal end of the implant bed.
 5. The implant delivery device according to claim 1, further comprising a pull wire to pull the rolling membrane proximally.
 6. The implant delivery device according to claim 5, wherein the slitter is in the same longitudinal diametral plane through the device as is the pull wire.
 7. The implant delivery device according to claim 1, further comprising a longitudinal shaft, wherein a proximal end of the outer sleeve is attached to a collar that slides proximally over the longitudinal shaft.
 8. The implant delivery device according to claim 7, wherein the longitudinal shaft defines a guidewire lumen.
 9. The implant delivery device according to claim 7, wherein the inner sleeve and the slitter are bonded to the longitudinal shaft proximal of the implant bed.
 10. The implant delivery device according to claim 1, wherein the slitter is a wire that runs an entire length of the implant bed, then passes radially outwardly through a hole in the inner sleeve and runs back proximally between the inner sleeve and the outer sleeve to a point proximal of the implant bed.
 11. The implant delivery device according to claim 1, wherein the rolling membrane comprises a cold-drawn polyethylene terephthalate material. 